Sex in Film

I'm currently watching the film Shortbus by John Cameron Mitchell. I saw the trailer a few times and it looked intriguing- a story about a NYC subculture, a topic which has always been alluring to me in some fashion. I've always loved NYC and people who live there have some kind of ownership of it that is hard to really understand from the outside- and makes me a little envious, if I'm honest.

According to the trailer, Shortbus is about a sex counselor of sorts on a quest for her first orgasm. In her quest, she connects with assorted societal misfits who gather at a place called Shortbus, this in reference to the preferred means of transporting "the gifted and challenged." The trailer promised interesting characters, and, so far, that has been the case. The characters are not just interesting, but likeable and quirky and human. But it also promised sex, and there is a LOT of it in the film. Some would say such a forthright portrayal of sex "honest" and maybe "daring" or even "vulnerable." Others might prefer terms like "exhibitionist" or "shocking" or "pornographic." I haven't finished watching it yet, but I'm kind of leaning towards Shortbus being appropriate in this case to the story the film sets out to tell. But I'm not sure, and I have a number of friends who would probably question my morality because of it. Now whether or not it is necessary to make a blatant film about sex is another question entirely. But I do think that there is an audience for almost every film, and I don't think that everyone has to be comfortable with every film that's out there. I mean, I'm not comfortable with Shortbus, but I'm trying to be as objective about it as I can be. It's clearly not meant for mass consumption, and I think that means that it can be interpreted differently than if it were a mainstream studio picture.

I am going somewhere with this, and I will express that in the form of some questions this movie has me asking:
Is it ever appropriate at all to portray explicit sex acts (ESA) in film? Does having well-developed characters and a well-thought-out plot soften the inclusion of ESA in a film? Does it matter whether or not said acts are inside or outside of a committed relationship? Can ESA actually be used creatively and naturally to move a story along?
American culture is notorious for being uptight about sex. But you have to draw a line somewhere, don't you?
Don't you?